1. Field of the Invention
Illustrative, non-limiting embodiments of the present invention generally relate to a silicon wafer break pattern formed by etching weak spots along a silicon wafer scribe line, a silicon substrate obtained by breaking the wafer according to the break pattern, and a method of creating the break pattern.
2. Description of the Related Art
A related method of dividing a silicon wafer into chips of a desired size will be described below in conjunction with FIGS. 8(a) to 8(c) and 9(a) to 9(c). FIGS. 8(a) to 8(c) illustrate a mask pattern 5 and break patterns in a horizontal direction of the wafer, and FIGS. 9(a) to 9(c) illustrate a mask pattern 5 and break patterns in a vertical direction of the wafer.
In the method of dividing the silicon wafer, a break pattern is formed on the silicon wafer by etching through-holes 1 in the horizontal direction along a horizontal scribe line L1 (FIG. 8(b)) and by etching a through-holes 1 in the vertical direction along a vertical scribe line L2 (FIG. 9(b)). The remaining portions of the silicon wafer between adjacent through-holes 1 on the scribe lines L1 and L2 constitute weak spots 2 of the break patterns. Subsequently, when an external force is applied along the scribe lines L1 and L2, the weak spots 2 break, and the silicon wafer is divided into a plurality of chips. FIG. 8(c) shows the shape of one edge of the chips when the wafer is broken along the horizontal scribe line L1, and FIG. 9(c) shows the shape of one edge of the chips when the wafer is broken along the vertical scribe line L2.
The shape of the through-holes 1 is determined by the anisotropy of the etching process when the silicon wafer is perforated by the etching process. Specifically, the silicon wafer comprises single-crystal silicon having a crystal structure that is difficult to etch in a first direction and that is easy to etch in a second direction.
For example, assume that the silicon wafer has a crystal structure having (110) planes and (111) planes. If the silicon wafer is etched with a 40% by weight potassium hydroxide solution, the two (111) planes perpendicular to the (110) plane are difficult to remove via the etching process, and the planes respectively inclined 30° to the two (111) planes are easy to remove via the etching process. For a general discussion of crystal structures, reference can be made to S. Wolf et al., Silicon Processing for the VLSI Era, Vol. 1, pages 1-5 (1986), which is incorporated herein by reference for all purposes.
If one of the (111) planes is then aligned at 0° on the (110) plane, the other (111) plane is aligned at 70.53° on the (110) plane. Also, the through-holes 1 formed in both the horizontal and vertical directions will form parallelograms, each having an acute angle of 70.53°. In order to form such through-holes 1, a mask pattern 5 (i.e. a pre-etching pattern) is used which has rows of parallelogram-shaped openings (or windows) 4 as shown in FIGS. 8(a) and 9(a). The shape of the windows 4 correspond to the shape of the through-holes 1, and the intervals between the openings 4 correspond to the weak spots 2. Also, the mask pattern 5 is formed on the wafer surface with a resist film, and the silicon exposed through the openings 4 is removed by wet etching.
As a result of the wet etching, the through-holes 1 are formed in the thickness direction of the wafer at the locations of the openings 4, and the break patterns (post-etching patterns) comprising the parallelogram-shaped through-holes 1 and weak spots 2 are formed as shown in FIGS. 8(b) and 9(b).
However, as shown in FIGS. 8(c) and 9(c), when the silicon wafer is divided along the break patterns described above, the location and shape of the breaks at the weak spots 2 cannot easily be made in a uniform manner. Specifically, after the silicon wafer is divided, a substantial amount of minute particles of waste and debris 6 is produced. Accordingly, the waste 6 must be carefully removed after the wafer is broken into multiple silicon substrates or chips. However, removing the waste 6 is extremely time-consuming and significantly decreases the manufacturing efficiency of the substrates or chips. Furthermore, if the waste 6 is not sufficiently removed, the remaining waste 6 leads to defects in the final finished product. For example, if an ink path substrate of an inkjet recording head is manufactured from a silicon substrate, waste 6 in the ink path of the substrate can interfere with ink flow, clog a nozzle, or cause other problems. Also, when a thin film is formed on the silicon substrate, any remaining waste 6 can cause defects and thus reduce the yield.
One way to reduce such waste 6 is to reduce the number of weak spots 2. This can be achieved by enlarging the through-holes 1 forming the break pattern in the direction of the scribe line L1 or L2. However, since the through-holes 1 are parallelograms having two (111) planes, enlarging the parallelograms also makes the scribe line L1 or L2 wider. When the scribe line L1 or L2 is widened, the number of silicon substrates that can be produced from a single wafer is reduced, and the high cost silicon wafers are inefficiently utilized. Furthermore, the production cost of the chips is substantially increased.
To avoid the above problem, long, narrow through-holes 1 may be formed. However, in such case, a substantial possibility exists that the through-holes 1 may not completely pierce the wafer due to the silicon wafer thickness and the angle at which the etching process etches silicon from the wafer.
Therefore, the above problems cannot be practically overcome by increasing the size of the parallelogram-shaped through-holes 1 or to make long, narrow (slender) through-holes 1.